On the Necessity of Rational Velocities: a Gedankenexperiment

In the present contribution we propose a gedankenexperiment in which the restriction of rational values on the velocities emerges as a necessary condition from Classical Electromagnetism and Quantum Mechanics. This restriction is shown to be intimately connected to Dirac's electric charge quantization condition.Comment: 4 pages IFUSP/P-105

N-loop Treatment of Overlapping Diagrams by the Implicit Regularization Technique

We show how the Implicit Regularization Technique (IRT) can be used for the perturbative renormalization of a simple field theoretical model, generally used as a test theory for new techniques. While IRT has been applied successfully in many problems involving symmetry breaking anomalies and nonabelian gauge groups, all at one loop level, this is the first attempt to a generalization of the technique for perturbative renormalization. We show that the overlapping divergent loops can be given a completely algebraic treatment. We display the connection between renormalization and counterterms in the Lagrangian. The algebraic advantages make IRT worth studying for perturbative renormalization of gauge theories.Comment: 12 figures eps, 61 pages, final versio

Preparation of Schr\"{o}dinger cat states of a cavity field via coupling to a superconducting charge qubit

We extend the approach of Ref. [Yu-xi Liu, L. F. Wei, and F. Nori, Europhys. Lett. 67, 941 (2004)] for preparing superposition states of a cavity field interacting with a superconducting charge qubit. We study effects of the nonlinearity on the creation of such states. We show that the main contribution of nonlinear effects is to shorten the time necessary to build the superposition.Comment: arXiv admin note: text overlap with arXiv:1301.609

Stochastic coupling in two modes systems: the weak-strong coupling transition

We investigate the weak-strong coupling transition of two linearly coupled systems under the influence of a phase fluctuating coupling. In the weak coupling regime the exponential decay of quantum properties is well known. A different scenario occurs in the strong coupling regime, the inhibition of the dynamics which tends to "freeze" as the ration between coupling strength and average phase fluctuation time increase. Exciton-polariton oscillations and the self-trapping phenomenon in Bose-Einstein Condensate qualitatively illustrate the weak and strong regimes respectively

Towards the understanding of Decoherence on Ion Traps

Two mechanisms of decoherence in ion traps are studied, specially related to the experiment [Kielpinski et al., Science 291 (2001) 1013]. Statistical hypothesis are made about the unknown variables and the expected behaviour of the visibility of the best experimental pattern is calculated for each mechanism. Data from the experiment are analyzed and show to be insufficient to distinguish between them. We suggest improvements which can do this with slight modifications in the present facilities.Comment: 7 pages, 4 figures, submitted to Phys Lett

Axial Monopoles, The Quantization of Electric Charge and a Dynamical Discreteness of Space-Time

In the present contribution we show that the introduction of a conserved axial current in electrodynamics can explain the quantization of electric charge, preserving parity conservation, and introduces a dynamical discreteness into space-time.Comment: 9 page

Axial Currents in Electrodynamics P.C.R

In the present work we argue that the usual assumption that magnetic currents possess the vector structure characteristic of electric currents may be the source of several difficulties in the theory of magnetic monopoles. We propose an {\it axial} magnetic current instead and show that such difficulties are solved. Charge quantization is shown to be intimately connected with results of theories of discrete space time.Comment: 9 pages IFUSP/P-105

Aspects of the competition between atom-field and field-environment couplings under the influence of an external source in dispersive Jaynes-Cummings model

We give a fully description of the dynamics of an atom dispersively coupled to a field mode in a dissipative environment fed by an external source. The competition between the unitary atom-field (which leads to entanglement) and the dissipative field-environment couplings are investigated in detail. We find the time evolution of the global atom-field system for any initial state and we show that atom-field steady state is at most classically correlated. For an initial state chosen, we evaluate the purity loss of the global system and of atomic and field subsystems as a function of time. We find that the source will tend to compensate for the dissipation of the field intensity and to accelerate decoherence of the global and atomic states. Moreover, we show that the degree of entanglement of the atom-field state, for the particular initial state chosen, can be completely quantified by concurrence. Analytical expression for time evolution of the concurrence is given.Comment: 19 pages, revtex4, 3 figure

Universality of finite time disentanglement

In this paper we investigate how common is the phenomenon of Finite Time Disentanglement (FTD) with respect to the set of quantum dynamics of bipartite quantum states with finite dimensional Hilbert spaces. Considering a quantum dynamics from a general sense, as just a continuous family of Completely Positive Trace Preserving maps (parametrized by the time variable) acting on the space of the bipartite systems, we conjecture that FTD happens for all dynamics but those when all maps of the family are induced by local unitary operations. We prove this conjecture valid for two important cases: i) when all maps are induced by unitaries; ii) for pairs of qubits, when all maps are unital. Moreover, we prove some general results about unitaries/CPTP maps preserving product/pure statesComment: 7 pages and 2 figures. New title. Improved version! Comments are welcom

Multipartite entanglement control via Quantum Zeno Effect

We develop a protocol based on 2M pairwise interacting qubits, which through Quantum Zeno Effect controls the entanglement distribution of the system. We also show that if the coupling constants are different the QZE may be used to achieve perfect entanglement swap